The present invention relates to flow meters in general, and in particular to flow meters that employ a wedge-shaped flow restricting element producing a pressure drop within the flow meter to indicate the volume of fluid flowing through the flow meter.
The use of wedges to create a pressure drop in flow meters for measurement of the volume of fluid passing through a flow meter is known in the art. Wedge-shaped flow meters are described in U.S. Pat. No. 4,237,739 issued on Dec. 9, 1980, U.S. Pat. No. 4,926,698 issued on May 22, 1990, and U.S. Pat. No. 6,672,173. The '739 patent describes a flow meter using a single wedge affixed to the internal wall of the flow meter whereas the '698 patent describes a flow meter having two opposing wedges mounted on opposite sides of the flow meter interior wall. Either arrangement creates an opening within the flow meter having a reduced cross-sectional area in the flow-path of the fluid thereby creating a pressure differential on opposite sides of the wedge or wedges. The pressure differential created on opposite sides of the wedges has a known mathematical relationship to the flow rate of the fluid passing there through, and as long as the cross-sectional area of the opening at the wedge is constant, the fluid flow measurements are very accurate. The '173 patent discloses A flow meter for measuring the volume of fluid flowing through the meter includes an inner cylindrical tube through which the fluid flows and an outer cylindrical tube tending over the inner cylindrical tube. With this meter a flow restriction member is mounted to an inner surface of the inner cylindrical tube for restricting the flow of fluid through the inner cylindrical tube and process a pressure drop in the fluid as it flow past the flow restriction member.
FIG. 1 shows a typical prior art flow meter 10 shown in cross-section. Flow meter 10 generally comprises a tubular housing 12 having a longitudinal passageway 14 in which a wedge-shaped member 16 is affixed to the inner wall 18 of housing 12 thereby creating at apex 20 of wedge 16 a restricted cross-sectional area represented by dimension D. At least two ports 22 are defined by housing 12. One of ports 22 is positioned upstream from wedge 16 and the other ports 22 is positioned downstream from wedge 16. Ports 22 are in fluid communication with the interior flow through passage 14 thereby permitting the detection of the pressure differential induced by wedge 16 restricting fluid flow through flow meter 10.
Nevertheless, fluid flow conditions under which the flow meters are used are variable and tend to change. Specifically, temperature changes and changes in the pressure of the fluid being measured cause the diameter of the passageway through the flow meter to expand and contract. Consequently, the cross-sectional area between the wedge apex and the flow meter wall opposite the wedge does not remain constant. Small changes in the flow meter passageway diameter or the distance between the wedge apex and the wall opposite from the wedge can make substantial changes in the pressure drop of the fluid flowing past the wedge. Consequently, these changes introduce unwanted errors in the calculated volume of fluid flowing through the meter.
Thus, there is a need within the industry for a torus 360 degree wedge-type flow meter where changes in the pressure and temperature of the fluid being measured by the flow meter will minimally affect the formed internal wedge element. The torus wedge is a significant departure from the traditional orifice plate technology and an enhancement of current wedge technology. The torus wedge flow meter will offer a fluid profile which does not generate fluid phase separation within the flow stream.